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Physiology Part 2 > Lec 33 pulmonary circulation > Flashcards

Lec 33 pulmonary circulation Flashcards

1
Q

What is role of pulmonary circulation?

A
  • carry de-ox blood from RV to alveoli and return ox blood to LA
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2
Q

What is the surface area for pulmonary vessels

A

125 m2

huge surface area

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3
Q

What is the struct of pulmonary vessels?

A
  • thin walled vessels, distensible
  • can handle entire CO from RV without increase in pressure
  • low pressure, low resistance
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4
Q

what is pressure in pulmonary vessels

A

5L/min

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5
Q

is pressure high or low in pulmonary circulation? what about resistance?

A
  • low pressure

- low resistance

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6
Q

What is systolic PA pressure?

A

25 mmHg [compared to SBP 120 mmHg]

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7
Q

what is diastolic PA pressure?

A

10 mmHg [compared to DBP 80 mmHg]

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8
Q

What is equation for flow?

A

Flow = Pressure gradient/Resistance

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9
Q

What is PVR? Equation?

A

pulmonary vascular resistance
PVR = pressure differential between pulm artery and LA pressures / Flow
= mPAP - mLAP/CO

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10
Q

How is pulmonary blood flow regulated?

A
  • by altering resistance of arterioles

- due to change in tone of arteriolar smooth muscle

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11
Q

What is unique about pulmonary vascular structure/regulation?

A
  • even smaller pulmonary arterioles have smooth muscles in their walls
  • all capable of vasoconstriction
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12
Q

What is most important mediator of vasoconstriction?

A

partial pressure of O2 in alveolar gas P[AO2]

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13
Q

What happens to pulmonary blood vessels in response to low alveolar Po2?

A
  • vasoconstriction via arteriolar smooth muscle
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14
Q

What happens to non-pulmonary vascular beds in response to low PO2? what about pulmonary vascular?

A

non-pulmonary: dilate with low PO2

pulmonary: constrict with low PO2

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15
Q

What is hypoxic vasoconstriction?

A
  • a protective mechanism
  • pulmonary arteries/arteriole smooth muscles constricts/contracts in low alveolar PO2
  • decrease perfusion [Q] to poorly ventilated [V] area so reduce V/Q mismatch by directing blood flow away from damaged or poorly ventilated alveoli
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16
Q

What 2 things cause generalized hypoxic vasoconstriction?

A
  • diffuse lung disease

- high altitude

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17
Q

What is the cellular mech of hypoxic pulmonary vasoconstriction?

A
  • at low alveolar PO2 [less than 70 mmHg]
  • inhibition of smooth muscle K+ channels
  • get depolarization
  • opens voltage gated Ca channels
  • get Ca influx -> smooth muscle contracts
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18
Q

What 3 things mediate hypoxic pulm vasoconstriction?

A
  • NO [dilator]
  • endothelin [constrictor]
  • arachidonic acid products [PGI2, TXA2] [dilator]
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19
Q

What is role of NO in hypoxic vasoconstriction?

A
  • NO inhibits hypoxic vasoconstrction
  • activates cGMP –> relaxes smooth muscle
  • causes vasodilation and anti-proliferation
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20
Q

What is nitric oxide synthase [NOS]?

A
  • synthesizes NO from L-arginine

- affected by low PO2

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21
Q

What is endothilin?

A
  • vasoconstrictor and causes proliferation

- plays role in hypoxic pulm vasoconstriction

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22
Q

what is role of PGI2 [prostacyclin] in hypoxic vasoconstriction?

A
  • activates cAMP

- causes vasodilation and antiproliferation

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23
Q

What happens in high altitude to PO2, vasoconstriction/dilation, PVR, etc?

A
  • reduced barometric P –> decrease in inspired PO2 –> low alveolar PO2
  • get global vasoconstriction
  • increased PVR
  • over time causes RV pressure overload and hypertrophy
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24
Q

What happens in fetal circulation to PO2, PVR, etc?

A
  • global vasoconstriction due to low alveolar PO2
  • high PVR
  • pulm blood flow is only 15% of CO
  • at birth when first breaths, increases alveolar PO2 to 100 mmHg
25
Q

What is order of size Pa [arterial], PA [alveolar], Pv [venous] in zone 1 [apex of lung]?

A

PA> Pa > Pv

alveolar > arterial > venous

26
Q

What is order of size Pa [arterial], PA [alveolar], Pv [venous] in zone 3 [base of lung]?

A

Pa > Pv > PA

arterial > venous > alveolar

27
Q

What is order of size Pa [arterial], PA [alveolar], Pv [venous] in zone 2 [middle of lung]?

A

Pa > PA > Pv

arterial > alveolar > venous

28
Q

What happens in zone 1?

A
  • gravitational effect causes lower arterial P than alveolar [atmospheric] P
  • causes pulm arterioles compressed
  • closure of capillaries
  • low blood flow
29
Q

Which zone of lung has least blood flow?

A

apex

30
Q

What two circumstances can cause blood vessels to close off and stop flow in zone 1?

A
  • arterial P gets lower: hemorrhage

- alveolar P gets higher: pos pressure on mechanical ventilator

31
Q

What happens to zone 1 if no blood flow there?

A
  • under-perfused
  • no gas exchange
  • becomes a physiologic dead space
32
Q

What happens in zone 2?

A
  • gravitational effect causes P arterial > P alveolar
  • alveolar P still higher than venous P
  • blood driven by arterial and alveolar pressure difference
33
Q

What is difference in the pressure difference that drives blood flow between zone 2 of lung and systemic vascular beds? What about zone 3 of lung?

A

zone 2 of lung: P arterial - P alveolar

systemic: P arterial - P venous

zone 3 of lung: P arterial - P venous

34
Q

What happens in zone 3 of lung?

A
  • gravity increases P arterial and P venous

- blood flow drive by P arterial - P venous

35
Q

What zone has highest blood flow in lungs?

A

zone 3

36
Q

What is a physiologic shunt in lungs?

A

portion of CO diverted/ re-routed bypassing alveoli

37
Q

What is bronchial blood flow? where does it drain?

A

blood supply to conducting airways, drains directly to LA

38
Q

What does coronary blood flow drain? via what veins?

A

drains directly into LV through thebesian veins

39
Q

What accounts for PO2 arterial being slightly less than PO2 alveolar?

A

physiologic shunt so some portion of blood bypasses alveoli and doesn’t get oxygenated and thus dilutes the oxygenated blood in the arteries

40
Q

What 2 blood flows part of physiologic shunt?

A
  • bronchial blood flow

- coronary blood flow

41
Q

What is right to left shunt?

A
  • direct flow of blood from right side of heart to left side of heart that never passes via alveoli/lungs so never gets oxygenated
42
Q

What is hypoxemia?

A

low PO2 in arterial blood

43
Q

Can hypoxemia be corrected by inhaling higher inspired O2?

A

No! shunted blood will dilute normally ox blood no matter how how alveolar PO2 is

44
Q

What will higher fraction inspired O2 do to right left shunt?

A
  • will increase dissolved O2 in capillary blood

- will not change total O2 content in blood b/c shunt is diluting it out

45
Q

What happens to arterial PCO2 in right to left shunt?

A

stays the same

46
Q

What do central chemoreceptors react to?

A
  • sensitive to changes in arterial PCO2

- slight increase in arterial PCO2 –> increases ventilatory rate to get rid of extra CO2

47
Q

When do chemoreceptors for O2 get activated? Are they more or less sensitive than chemoreceptors for CO2?

A
  • less sensitive to changes in O2 than CO2

- O2 receptors activated at PO2 < 60 mmHg in arteries

48
Q

What is left to right shunt?

A
  • ox blood from left side of circulation enters right side
  • oxygenated blood re-circulated through lungs
  • pulmonary blood flow increases as part of left CO enters right side
49
Q

What 3 things can cause left to right shunt?

A

ASD
VSD
Patent ductus arteriosus

50
Q

What happens to pulmonary blood flow in left to right shunt?

A

pulm blood flow increases since part of left CO enters right side

51
Q

What is PO2 on right side heart in left to right shunt?

A
  • abnormally elevated PO2 in right heart
52
Q

Does left to right shunt cause hypoxemia? right to left shunt?

A
  • right to left causes hypoxemia

- left to right does not cause hypoxemia

53
Q

What happens to Valveolar/Q in shunt vs dead space?

A
  • lower V/Q in shunt

- higher V/Q in dead space

54
Q

What is normal PO2 and PCO2 in alveoli?

A 
PO2 = 100
PCO2 = 40
55
Q

What normal PO2 and PCO2 in capillary?

A 
PO2 = 40
PCO2 = 45
56
Q

What is ventilation like in shunt vs deadspace? what about perfusion?

A

shunt: no ventilation, have perfusion so blood not getting oxygenated

dead space: no perfusion, have ventilation but its wasted because there is no blood to oxygenate

57
Q

What is V/Q ratio in shunt?

A

V/Q ratio = 0 because there is no ventilation

58
Q

What is V/Q ratio in dead space?

A

V/Q ratio = infinity because such little perfusion

59
Q

What is alveolar PCO2 in case of dead space?

A

PCO2 = 0 in alveoli because there is no perfusion so no gas exchange so no CO2 to excrete

Physiology Part 2 (19 decks)

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